NITROGLYCERIN: VENOUS VASODILATOR (ORGANIC NITRATES)
GENERAL DESCRIPTION
Nitroglycerin is also known as glyceryl nitrates (GTN). It is a nitrodilators. Nitroglycerin is the prototype of nitrodilators. Sublingual nitroglycerin is the most frequently used agent for the immediate treatment of angina.
GENERIC NAME: Glyceryl nitrate
BRAND NAME: Nitrostat, Nitro-bid, Nitro-quick
MECHANISM OF ACTION
Nitrodilators are divided into two types according to the release of NO
- release NO spontaneously
- require enzymes to form NO.
Nitroglycerin requires glutathione S-transferase enzyme to be denitrated. This process release free nitrite ions which then converted to nitric oxide NO. This nitric oxide is potent activator of guanylyl cyclase enzyme (GC) which is soluble in smooth muscle. This guanylyl cyclase (GC) convert GTP into cGMP. This intracellular cGMP block the calcium to enter into the cells tends to decrease the calcium levels in the cells which then cause smooth muscles relaxation. The cGMP also activates protein kinase C (PKC) which further activates phosphatase enzymes. This phosphatase inactivates myosin light chain which further take part in relaxation of smooth muscles. The major effect of GTN is on venous smooth muscles. These actions tend to decrease the venous return by increase venous capacitance. This decrease the cardiac output and myocardial oxygen demand.
PHARMACOKINETICS
The liver has high level of organic nitrate reductase which immediately inactivates the nitroglycerin. Therefore its oral bioavailability is very low approximately < 10-20%. To avoid this first-pass effects nitroglycerin is given sublingually to achieve therapeutic blood level rapidly within a few minutes. The total duration of action is 15-30 minutes. After absorption unchanged nitrates have 2-8 minutes half-life while metabolites of nitroglycerin has half-life up to 3 hours. It is excreted by urine excretion through kidneys in the form of glucuronide.
INDICATIONS
Hypertensive emergencies
Myocardial infarction
Angina
Acute coronary artery spasm
Pulmonary edema
CONTRAINDICATIONS
Elevated intracranial pressure
SIDE EFFECTS & ADVERSE EFFECTS
Hypotension
Tachycardia
Headache
Circulatory collapse
DRUG INTERACTION
Phosphodiesterase type-5 inhibitors potentiate the hypotensive effects of nitroglycerin and may cause myocardial infarction. Therefore these drugs are contraindicated with nitroglycerin.
Glyceryl trinitrate infusion reduce the effects of heparin.
Analgesic dose of aspirin increase plasma level of nitroglycerin given sublingually and may cause hypotension and headache.
Dihydroergotamine reduce antianginal effect of glyceryl nitrate
Glyceryl nitrate can safely give with calcium channel blocker, but cause hypotensive effects and faintness with diltiazem.
NURSING INTERVENTION
Enquire the complete health history of the patient including allergy, drug interactions, and family background of hypertension.
Monitor blood pressure and pulse before and during treatment.
Check lab test for CBC, blood glucose, BUN, creatinine, platelets, electrolytes, LFT
Arterial pressure should be monitored during treatment via intra-arterial recording.
Observe patients for possible s/s of edema or congestive heart failure.
PATIENT EDUCATION
Avoid taking alcohol while taking medicine.
Instruct the right dose and timings of medicine.
Inform the patients about the possible side effects
Advice to take care and slow change of posture due to dizziness and danger of fall or injuries
Medicine may cause dizziness, don’t drive or perform alertness activities.
Report health professional immediately if dermatological adverse effects seen.
Do not breast feed while taking the medicine.
Educate patient healthy life style choice to reduce hypertension such as dietary intake of sodium and cholesterol, exercise, smoking cessation etc.